Many wastewater treatment plants (WWTPs) utilize an activated sludge process (ASP—primarily consisting of suspended growth biological treatment reactors and secondary clarifiers) designed to operate at mixed liquor suspended solids (MLSS) concentrations of approximately 3,000 mg/L or lower. MLSS is the suspended biomass that grows on the contaminants in wastewater as the contaminants are degraded. It is considered however that it becomes cost prohibitive to operate an ASP process at substantially higher MLSS concentrations, such as approximately in the range of 5,000 mg/L to 6,000 mg/L or higher. On the other hand while the newer membrane bioreactor (MBR) approach, in which solid-liquid separation is accomplished by micro- or ultra-filtration membranes, can cost effectively process higher MLSS concentrations, it is also understood implementing MBR becomes cost prohibitive in the range of approximately 5,000 mg/L to 6,000 mg/L, and below.
Aeration is not a limiting factor to operating ASPs at the higher MLSS levels since mechanical or fine bubble diffused aeration is still cost effective at MLSS concentrations upward of 10,000 mg/L. However, a factor that does inhibit use of ASP at these higher MLSS concentration levels is the capital cost of secondary clarifiers, which increases non-linearly as the MLSS concentration approaches and exceeds 5,000 mg/L.
Therefore it is considered useful to provide systems and methods that increase the operational capacity of existing WWTPs using ASP approaches in a cost effective manner.